Cocktail Dress

The length of a cocktail dress is long, often touching the ankle. When it is about 5 cm (2 inches) above the ankle it is called tea length and when it is almost touching the ankle it is called ballerina length, although ballerina length dresses usually fall into the evening gown category.
At semi-formal occasions, a less elaborate, shorter-length cocktail dress may be worn. Prior to the mid 20th century this type of dress was known as late afternoon. When gentlemen are in business suits, ladies also wear dress suits or good afternoon skirt and dresses.
By the 1980s the criteria by which a garment was considered a "Cocktail Dress" was not its length, but its level of sumptuousness.
In the mid-20th century, some couturiers began describing full-skirted cocktail gowns as "dancing costumes". These are suitable for formal dances but not for balls, or other white tie affairs, where ball gowns are worn.